1. Field of the Invention
This invention relates to the field of stump grinding machines, particularly with respect to the shaft assembly useful with a grinding wheel for grinding tree stumps. More specifically, it relates to such an assembly useful with a boom-end mounted stump grinder.
2. Description of the Related Art
It is known to provide a stump grinding apparatus to cut and dispose of tree stumps. The device finds use for agricultural applications, for proper lawn maintenance and care, and for site development. It is often required to lower a protruding stump to a level that is below grade so that it will not interfere with plowing, disking and other farm tasks. For pleasing appearance of residential lawns, stumps of dead and fallen trees must likewise be cut away to a point that is below grade to allow for soil to be placed thereover for seeding or planting. When used for site development, the apparatus removes the stumps, thereby permitting soil to be moved as needed.
Typically, such a device includes a rotatable grinding wheel having a plurality of cutting teeth disposed circumferentially about the wheel. The wheel can be powered by a chain drive, or by gear or belt, or may be at the end of a movable boom driven by a diesel or gasoline engine. The grinding wheel commonly encounters more than just wood when performing its tasks. The wheel may be brought into contact with rocks and all manner of buried debris, such as re-bar, wire, cinder block and other materials of construction. The stump grinding operation places tremendous radial and axial loads on the wheel, the drive shaft and other component parts associated with the wheel assembly.
One particular stump grinder is mounted on the end of an excavator boom and uses a self-contained diesel engine and a combination belt and gear drive to rotate the grinding wheel. The wheel is mounted on a drive shaft that is supported in a frame at the end of the boom. Grinders of this type are manufactured by Sneller Machine Co., Cleveland, Ohio, and are referred to as the Sneller Stump Mill. The drive shaft rotates in two sets of roller bearings. Because of the encounters with miscellaneous debris during grinding, the bearings are subject to tremendous lateral and axial stress. The bearings and grease seals are exposed to entanglement with wire that can become wrapped around the shaft and can damage or destroy the grease seals around the bearings, causing premature failure of the bearings. Furthermore, with improper tolerances and clearances between the rotating and non-rotating parts of the assembly, bearing wear can be substantial, thus necessitating shutdown and repair of the stump grinder. Because of the costs associated with the disassembly and repair of the equipment, and the associated non-productive time, ways are constantly being sought for reducing downtime.
It is an objective of the present invention to increase the length of the in-service time intervals for a stump grinder. Another objective is to reduce the time and expense for maintenance of a stump grinder.
These and other objectives and advantages will become apparent upon a reading of the description that follows.
The present invention relates to a boom-end stump grinder utilizing a shaft assembly providing maintenance-free service. The invention furthermore relates to an improved shaft assembly for use with a boom-end stump grinder.
The invention relates to a mounting arrangement for the cutter wheel of a stump grinder. The arrangement is a shaft assembly that comprises a shaft having an inboard end adapted to engage a rotational power source, and an outboard end distal from the power source. An inboard hub is mounted on the shaft for rotation therewith and an outboard hub likewise is mounted on the shaft for rotation therewith. Each hub includes a radially extending flange defining a gap between the two flanges to receive a cutter wheel. An annular cast iron shell surrounds the shaft and is separated therefrom by an inboard roller bearing and by a layer of lubricant. The shell is separated from the inboard hub by a labyrinth typically filled with grease. A second annular cast iron shell surrounds the shaft and is separated therefrom by an outboard roller bearing and a layer of lubricant. The shell is separated from the outboard hub by a second grease labyrinth. The shaft and hubs are rotationally movable with respect to the two cast iron shells. Typically, both the inboard bearing and the outboard bearing are non-adjustable double roller bearings. The labyrinths are located axially between the two cast iron shells and the respective inboard or outboard hubs. A gap is maintained between each of the shells and the shaft. This gap is no greater than about 0.100, and preferably no more than 0.080xe2x80x3, and is filled with lubricant supplied from the labyrinth. Likewise, a gap is maintained between each of the cast iron shells and an axially extending portion of the respective hub. This gap is no greater than about 0.150, and preferably no more than 0.125xe2x80x3, and contains lubricant supplied from the labyrinth. The length of the axially extending portion of each hub is at least about 1xe2x80x3.
In another aspect of the invention, a shaft assembly is adapted to be mounted on a stump grinder frame and comprises a cutter wheel secured between two hubs, the hubs mounted for rotation with a shaft. The shaft has an inboard end adapted to engage a rotational power source, and an outboard end. The two hubs comprise an inboard hub and an outboard hub, each hub including a radially extending flange defining a gap between the two flanges to receive the cutter wheel. An inboard cast iron shell surrounds the shaft and is separated from the shaft by an inboard roller bearing and by a layer of lubricant. The inboard shell is separated from the inboard hub by a grease labyrinth. An outboard cast iron shell surrounds the shaft, and is separated therefrom by an outboard roller bearing and by a layer of lubricant. The shell is separated from the outboard hub by a grease labyrinth. The two cast iron shells are adapted to be mounted in a frame at the end of the boom. Preferably, the inboard bearing and the outboard bearing are non-adjustable double roller bearings. A gap is maintained between each of the shells and the shaft of no greater than about 0.080xe2x80x3, and the gap is filled with grease supplied from the labyrinth. Similarly, a gap is maintained between each of the shells and an axially extending portion of the respective hub of no greater than about 0.125xe2x80x3, wherein the gap contains lubricant supplied from the labyrinth. The length of the axially extending portion of each hub preferably is at least about 1 inch. An annular sleeve engages and surrounds the outboard end of the shaft. The sleeve has a radially outwardly extending flange at one end thereof that abuts a shoulder on the shaft, and has external threads at the opposite end to receive a lock washer and nut. The shaft and sleeve are keyed to prevent rotational slippage of the sleeve on the shaft. The inner race of the outboard bearing is press fit on the outer surface of the sleeve and abuts the radially outwardly extending flange of the sleeve.